This invention relates to an injection molding machine for molding a melted resin into a product or a molded product.
An injection molding machine of the type described comprises a die section having a cavity which is opened or closed, an injection section for injecting a melted resin into the cavity to form a molded product in the cavity, a die-driving section for driving the die section to open or close the cavity and to eject the molded product from the cavity, and a control section for controlling the injection section and the die-driving section.
Heretofore, a conventional injection molding machine of a motor-drive type has widely been used wherein both the injection and the die sections are driven by a plurality of electric motors. More particularly, the injection section comprises a first motor for introducing the melted resin in the injection section and a second motor for injecting the melted resin into the die section. The die-driving section comprises a third motor for opening and clamping the die section and a fourth motor for taking out or ejecting the molded product from the die section. Thus, at least four electric motors are included in such an injection molding machine. In other words, any other motors may be included in the injection molding machine, although description will be mainly made about the first through fourth motors.
Taking the above into account, the first through fourth motors should be controlled by the control section so as to mold the melted resin into the molded product in accordance with a predetermined injection molding process. To this end, the control section must comprise four control units in correspondence to the first, the second, the third, and the fourth motors.
In order to reduce the number of control units, an improved injection molding machine is disclosed in Japanese Unexamined Patent Publication No. 97821/1985 (Tokkai Syo 60-97821). In this improved injection molding machine, the control section is implemented by a single control unit which is selectively coupled to the injection section and the die-driving section by a switching circuit. This means that the injection section and the die-driving section must be operated in a time division fashion. Therefore, both the injection and the die-driving sections are driven so that a first driving duration for the injection section is not overlapped with a second driving duration for the die-driving section.
However, it has been found out that a molded product of a high quality is not manufactured when the injection section and the die-driving section are driven in a time division fashion, as mentioned above. This is because it often occurs in such an injection molding machine that both the injection section and the die-driving section are simultaneously driven so as to avoid damages, such as a burr and a sink, which are inherent to the injection molding machine.